Evolution

Evolution is the process by which new species are slowly formed from pre-existing ones over a period of time. Both Charles Darwin and Alfred Wallace put forward the basis of current ideas about evolution. They independently developed the theory of evolution by natural selection and based their ideas on observations of variations in the population and the tendency for the size of the adult population to remain stable.

The theory is based on the following observations:

o All populations have some variation.

o The numbers of adults in the population tends to remain stable although large numbers of offspring may be produced.

From these two observations the following deductions were made:

o There must be a ‘struggle for survival’ amongst the offspring with only the ‘fittest’ surviving.’

o Some individuals that belonged to the same species may give rise to two different groups, which are sufficiently distinct to belong to two separate species.

When organisms evolve it is the molecules of DNA within them that have changed over time. DNA determines the structure of proteins, including enzymes, within the organism and this will affect the internal and external structure of the organism.

Comparing the structure of the proteins and DNA of different species now allows scientists to study the evolutionary links between them.